Bone marrow transplantation is a preferred clinical treatment for an expanding number of diseases. Donors and recipients of bone marrow are matched based on a complex group of cell surface proteins called the HLA (Human Leukocyte Antigen) system. While HLA class I A and B and HLA class II DRB1 are believed to be major antigens critical for matching, the system is highly polymorphic with a large number of alleles directing individual polymorphisms at each genetic locus. Although DNA methods currently provide the best level of matching for successful transplants, these methods are costly, labor intensive and limited in their ability to provide the refined resolution of HLA alleles necessary to optimize transplant outcome. In preliminary studies, we developed a new HLA-DNA Microarray methodology which has the potential to form a new technology base for a highly accurate, yet, efficient, practical and low cost assay system for clinical HLA typing. This Phase I proposal is designed as a proof-of-concept test to determine whether HLA- DNA Microarrays can achieve the accuracy and reproducibility of current DNA-methods as applied to high resolution typing of the class II DRB1 locus. The prototype HLA-DNA Microarray developed in preliminary work will be modified to improve efficiency, accuracy and sensitivity by optimizing the fluorescence signal generating system. The reagent system and methods for fabricating HLA-DNA Microarrays to perform high resolution (allelic level) typing of class II DRB1 loci will be designed and developed. High resolution class IIDRB1 Microarrays will be evaluated in a blinded trial using a set of 200 characterized samples from ethnically diverse individuals and the results compared with those obtained by current DNA methods. If successful, Phase I will demonstrate that the HLA-DNA Microarray technology is sound and can fulfill the requirements of a new, clinically important testing platform and set the stage for full-scale development of the complete HLA class I/class II HLA-DNA Microarray typing system in Phase II. The HLA-Microarray product will have immediate commercial utility in clinical laboratories supporting bone marrow and organ transplantation programs.